1. Field of the Invention
The present invention relates to apparatus to minimize noise and wear in blocking apparatus provided in a mold clamping system to prevent unintended movement of a first mold-carrying platen toward a second mold-carrying platen. More particularly, the present invention relates to the reduction of noise and wear in apparatus in which a blocking bar having a stepped outer surface is slidably carried in a platen bore by providing a non-metallic supporting bushing in the bore to eliminate wear between the blocking bar and the bar-receiving bore in the platen, and simultaneously to reduce the intermittent contact noise that results as the stepped bar passes through the bore.
2. Description of the Related Art
Machines such as presses, die casting machines, injection molding machines, and the like, generally include a movable platen that is supported for movement toward and away from a fixed platen to selectively bring molds or other shaping members carried by the respective platens into and out of engagement or contact. Many different approaches have been suggested to prevent unintended relative movement of the platens toward each other when a particular condition has been detected.
A common approach to preventing unintended movement of one machine part relative to another, such as a movable platen, is a limit switch or another form of position sensor that is adapted to sense the position of one of the parts and to disable the machine when the part has reached a predetermined position, or when a predetermined condition has occurred.
Another approach is to provide a notched or stepped bar that extends between the two parts to be maintained in spaced condition, such as mold-carrying platens, and to provide a rigid but movable blocking member that is adapted to be received in the notch or step formed in the bar, to thereby block movement of the platens toward each other when a predetermined condition occurs. In such an arrangement, it is necessary that the stepped bar be securely carried by one of the mold-carrying platens, and that the other mold-carrying platen have a bore to slidably receive the stepped bar and to maintain it in a properly aligned condition so that the blocking member can engage with one of the steps or notches and thereby prevent unintended relative movement of the platens.
In previously-employed stepped bar structures the metal-to-metal contact that is involved in such a construction results in metallic dust that constitutes a contaminant. Further, the introduction of a lubricant between the bar and bore to minimize friction and the generation of metallic dust is also undesirable because it also is a contaminant, especially in situations where sterile articles are being injection molded for medical purposes.
Finally, the notched structure of the stepped bar causes an objectionable staccato clicking sound as the bar passes through and within the bore.
It is an object of the present invention to overcome the above-described deficiencies in the presently-employed arrangements.
It is another object of the present invention to provide an arrangement in which a bushing is provided to slidably receive a notched bar and that does not require lubrication by foreign substances.
It is a further object of the present invention to provide a bushing for slidably receiving a stepped bar and that does not result in the generation of metallic dust.
It is a still further object of the present invention to provide a bushing for slidably receiving a stepped bar and that does not substantially transmit the intermittent sounds that result when the notched stepped bar is slidably moved through the metallic bore.